The present invention relates to an information recording medium such as an optical disk or the like on/from which data can be recorded/reproduced. The present invention also relates to an information recording apparatus and method for recording information on the information recording medium. Furthermore, the present invention relates to an information reproduction apparatus and method for reproducing information recorded on the information recording medium.
As one of information recording media, for example, a phase change type rewritable optical disk is known. When such optical disk is irradiated with a focused light beam, phase change marks are formed on the disk in accordance with changes in intensity of the light beam. That is, by controlling the light beam with which the disk is irradiated in correspondence with given recording data, that data can be recorded on the disk.
When data is reproduced from such optical disk, the optical disk is irradiated with a focused light beam. In this case, the light beam has lower laser power than that upon recording. When the disk is irradiated with the light beam, light reflected by the disk can be obtained accordingly. This reflected light contains components of phase change marks formed on the disk. That is, given data recorded as phase change marks on the disk can be reproduced by detecting this reflected light.
The specifications and merits of a DVD (Digital Versatile Disk)-RAM will be explained below. A rewritable optical disk on which data can be repetitively recorded at an arbitrary position and from which data at an arbitrary position can be reproduced, as described above, is known. As one of such optical disks, an internationally standardized rewritable optical disk (ISO/IEC16824) called a DVD-RAM having a diameter of 120 mm is known. On this DVD-RAM, a zigzag groove (this zigzag pattern will be referred to as a wobble hereinafter) and a flat portion called a land are formed, and data are recorded on both the groove and flat portion. More specifically, data are recorded in units of error correction code blocks (1 ECC block) each of which consists of 16 sectors containing 2,048 bytes per sector as in a DVD-ROM (ISO/IEC16448) as a read-only optical disk.
On this optical disk, address data are recorded in advance in units of sectors (physical sectors). These address data are recorded by embossed pits called CAPA (Complementary Allocated Pit Addresses). This CAPA is formed on a portion between the land and groove so that address information can be extracted even when an optical head is located on either the groove or land. Data are recorded in units of ECC blocks, but are continuously recorded in 16 physical sectors on an actual disk.
The optical disk is segmented into a plurality of zones in the radial direction, and each zone undergoes rotation control at a constant rotational speed. That is, rotation control adopts a ZCLV (Zoned Constant Linear Velocity) scheme. In this scheme, a given zone has equal numbers of sectors per round of a track. Upon comparison between a given zone and its outer neighboring zone, the number of sectors per round of a track in the outer neighboring zone is larger by 1 than that in the given zone. In a single zone, CAPA are aligned in the radial direction. As a result, since no embossed bits are formed in the radial direction of an area where target data is recorded, recording/reproduction can be prevented from becoming unstable due to the influence of embossed pits. However, in a different zone (across zones), CAPA aligned in the radial direction are disconnected. The zone width is determined in consideration of alignment of CAPA and format efficiency. For example, a zone width is determined as a range within which the number of sectors per round of a track does not increase.
In the DVD-RAM, since physical addresses are determined in units of sectors, data can be recorded at an arbitrary address on the disk, and can also be recorded without initialization. Since address information is always obtained in units of sectors, a seek time can be shortened, and if any defect is detected, such defect can be skipped in units of sectors. Hence, the DVD-RAM is suitable for recording random data.
The two-layered recording layer structure will be explained below. As a method of increasing the recording capacity per optical disk, a method of using the two-layered recording layer structure may be used. This follows a single-sided, two-layered structure adopted in a DVD-ROM as a read-only disk. A disk on which two recording layers are formed to be separated by a transparent layer is irradiated with light from a given side, and the light is focused on a desired one of the two recording layers to record data on the target recording layer or to reproduce data recorded on the target recording layer.
Problems of the two-layered recording layer structure will be explained below. In a two-layered disk, upon recording/reproducing data on/from a recording layer on the back side (back recording layer) viewed from the incoming direction of a light beam, a recording/reproduction light beam is transmitted through a recording layer on the front side (front recording layer). If the recording layer on the front side is of a ROM type, data are recorded in advance as embossed pits on the entire front recording layer. For this reason, the transmittance and reflectance of the front recording layer through which light which enters or is reflected by the back recording layer is transmitted is always nearly constant on the entire recording layer. By contrast, in case of a rewritable disk like a DVD-RAM (i.e., when the front recording layer is of a RAM type), an emboss area where data are recorded by embossed pits, a phase change recording area where data are recorded by phase change, and the like are present, and these areas have different transmittances and reflectances. Also, even in the phase change recording area, an amorphous area (recorded area) and crystalline area (non-recorded area) have different transmittances and reflectances. Such differences pose the following problems.
1. When both recorded and non-recorded areas are present on the front recording layer, since the intensity of recording light which is transmitted through the front recording layer and reaches the back recording layer varies between these areas, inter-recording marks formed on the back recording layer by this recording light become uneven, thus impairing recording stability.
2. When both recorded and non-recorded areas are present on the front recording layer, since the intensity of reproduction light, which is transmitted through the front recording layer, reaches the back recording layer, is reflected by the back recording layer, and is transmitted through the front recording layer again, varies between these areas, errors readily occur in a reproduction signal. Furthermore, since the reflectance of the front recording layer changes, a reproduction signal suffers an offset, thus impairing reproduction stability.
An area of the DVD-RAM where embossed pits like CAPA are recorded is an information recording inhibited area, and is always in a non-recorded state. The substrate shape of the CAPA area is an emboss, and has different optical conditions such as scattering of light and the like from those of a recorded area where a groove is formed. That is, such area also has a different transmittance. Furthermore, in case of a DVD-RAM, since CAPA areas are recorded in units of sectors, the innermost zone has 25 CAPA areas per round of a track, and the outermost zone has 59 CAPA areas per round of a track. When the two recording layers having such structures are adhered without any constraints, recording/reproduction stability suffers.
Problems that pertain to format efficiency of a DVD-RAM will be explained below. In a method of recording address data using embossed pits in units of sectors like a DVD-RAM, address fields (header fields), buffer fields, guard fields, and the like are required in units of sectors. The buffer field is formed to absorb a change in actual sector length on the disk, which is caused by rotational variations of the disk, eccentricity upon rotation, and the like. The guard field is formed to cope with random shift of a recording position and deterioration of the leading and trailing ends due to recording. In this manner, the DVD-RAM requires various fields in addition to fields for recording user data. This causes considerable format efficiency drop of the DVD-RAM compared to the DVD-ROM. More specifically, format efficiency of the DVD-RAM is about 10% smaller than the format efficiency of the DVD-ROM.
Problems associated with CAPA in seamless recording will be explained below. On the DVD-RAM, a large zone width is assured to align CAPA, and the recording frequency varies largely between neighboring zones. For this reason, when large-size data such as video data or the like are to be continuously recorded, the time required for switching the recording frequency is required in units of zones. As a result, problems such as transfer rate drop, difficulty in seamless recording, and the like are posed.
The necessity and problems of a training pattern will be explained below. As an optical disk has a higher recording density, and a lens has higher NA, deterioration of a reproduction signal due to the influences of crosstalk between neighboring tracks, intersymbol interference, disk tilt, and the like is not negligible. As a method devised to solve this problem, a waveform equalization condition is determined by reproducing a training pattern as known sequence data on a disk, thus compensating for deterioration of a reproduction signal. Also, a method of measuring any tilt of a disk using such condition and reproduction information itself of known data is available. In these methods, a training pattern must be recorded beforehand on the disk. But when such training pattern is locally inserted in a recording field, the storage capacity decreases. Furthermore, when the training pattern is formed in a recording field, it becomes difficult to specify the position of the training pattern upon recording/reproduction, and such pattern disturbs continuous recording.
Furthermore, a problem of the embossed pit locations of a DVD-RAM will be described below. An information recording method on an optical disk includes a CLV scheme that maintains a constant linear velocity upon scanning a beam spot even at different radial positions of tracks during recording/reproduction, and a CAV scheme that maintains a constant rotational speed of the disk even at different radial positions of tracks during recording/reproduction. In the CLV scheme, an even recording density can be achieved on the entire disk. By contrast, in the CAV scheme, although outer tracks have larger lengths, since inner and outer tracks have equal recording capacity, the recording density lowers toward the outer periphery of the disk. Therefore, if the recording density of an innermost track remains the same, the CLV scheme can assure a larger recording capacity on the whole disk than the CAV scheme. For this reason, a conventional DVD-ROM or the like adopts the CLV scheme. However, a conventional DVD-RAM adopts the ZCLV scheme since it cannot adopt the CLV scheme owing to the problem of the embossed pit locations to be described later.
On the DVD-RAM, neighboring embossed pit sections are aligned in the radial direction so as to inhibit a track that radially neighbors the embossed pit section from becoming a data recorded portion, in consideration of tracking and a problem of signal crosstalk. When neighboring embossed pit sections are juxtaposed in the radial direction, the inner and outer tracks of the disk have the same number of sectors per round of a track. Such locations are the same as those in the CAV scheme. Therefore, in the method of locating the embossed pit sections in this way, the recording density in the track direction lowers toward the outer periphery of the disk. For this reason, the DVD-RAM adopts the ZCLV recording scheme that segments the entire recording layer of the disk into some zones in the radial direction. In the ZCLV scheme, the numbers of sectors per round of a track are equal in each zone, i.e., each zone adopts the CAV scheme, but the number of sectors per round of a track increases in outer zones, thus increasing the recording density. However, in the ZCLV recording scheme, inner zones have lower recording density in the track direction than in outer zones. Furthermore, since the recording frequency between neighboring zones jumps largely, a zone change time is required upon continuously recording large-size data such as video data or the like, resulting in transfer rate drop and difficult seamless recording.
On the DVD-RAM, since each CAPA as address information formed as embossed pits is formed between land and groove tracks, the address information is reproduced at the tail of a beam spot that tracks the land or groove. For this reason, it is difficult to form embossed pits for obtaining a precise reproduction signal, and to adjust an optical head for reading a signal, resulting in an increase in cost.
Since the DVD-ROM and DVD-RAM have considerably different formats due to the different recording/reproduction schemes mentioned above, the load on the apparatus or the like becomes heavy if compatibility is to be assured.
To solve this problem, as a method of recording data without forming address information on an optical disk in units of sectors, a groove on the optical disk is wobbled to record address information as an FM signal, and data are recorded in units of error correction blocks based on the address information, as in, e.g., a CD-R or CD-RW. In a DVD-R, address data is recorded using land prepits which do not impose any influences upon reproduction by a DVD-ROM drive. In either case, since the address of each error correction block is determined only after data is recorded, it is difficult to efficiently record data at an arbitrary position. Also, a recording end process is required after data recording, and dummy data are recorded over several hundred tracks, thus requiring an extra time in data recording. Such recording scheme is suitable for recording continuous data such as video data, but is not suitable for recording small fragments of data such as computer file data.
A group of inventors of the present invention suggests that manages sector addresses using index headers and wobbles before physical formatting, and manages addresses by providing address information in the header of the written recording field after physical formatting or recording. This technique solves the problem of embossed pit locations. However, the present inventors have been studying to further increase the recording density.
In Jpn. Pat. Appln. KOKAI Publication No. 09-27127, a track for one round is broken up into a sector and a plurality of segments which are different from the sector, and segment addresses are recorded in advance in the track. However, with this technique, since the addresses are managed using the sector and segments, management information increases in amount.